Case study : Global Warming

This case study on the potential damage from global warming
consists of the following parts:

1. This page, which is a summary of the scenarios for the effects of
global warming and a short discussion on how we should try to choose
between the scenarios.

2. We will examine global warming and the alternate scenarios using
two different views; the systems
view and the games view.
You have already used these two views previously. In the systems view,
we will focus on comparing positive and negative feedback controls and
in the games view we evaluate different scenarios in a game against
nature.

Feedback Cycles in Global Warming

One of the causes of global warming, or more generally, global climate
change is increased atmospheric CO2 that comes from anthropogenic sources.
Human activity is increasing the release of CO2 into the atmosphere by
burning fossil fuels, burning forests, deforestation and destruction of
the soil, along with other activities. This pulse of CO2 into the atmosphere
is a perturbation and the earth system will respond with some changes.
Our focus is to attempt to identify important responses and determine
whether these responses will counter the increase in CO2 or temperature,
or whether the response will exacerbate the change.

In a systems view of this system, we are looking for feedback cycles
that are either positive or negative (Figure 1). A negative feedback cycle
will resist change with compensatory flows in other parts of the system.
Conversely, a positive feedback will accelerate the rate of change.

Figure 1. Several possible feedback cycles for global warming. The
details are discussed in the text below.

There is a negative feedback cycle involving CO2, temperature and
algae.

increased CO2 causes surface temperature to rise

which leads to increased algae growth rates in the ocean,

which depletes atmospheric CO2

thus countering the rise in atmospheric CO2.

There is a positive feedback cycle involving air temperature, CO2
and soil organisms.

increased CO2 causes surface temperature to rise

increased temperature causes soil organisms to respire faster

faster respiration converts more soil organics to CO2

thus accelerating the cycle of CO2 input.

There is another positive feedback involving surface albedo of glaciers
and temperature.

increased temperature causes glaciers to melt

the loss of reflective surface of the glacier leads to more absorption
of sunlight

more absorption leads to higher temperatures

thus accelerating the melting and temperature rise

It is crucial that we understand these cycles and the potential interaction
between these cycles.The negative feedback cycles will lead to controlling
or minimizing temperature gain, whereas positive feedback processes will
contribute to acceleration of the problem. If we are very lucky, there
may be very strong negative feedback controls that will buffer human impact.
If we are less lucky, a slight anthropogenic change may trigger a set
or processes that will cause a shift in the processes that control surface
temperature. In terms of resilience; if the overall global system is very
resilient, human perturbation may be quickly fixed, on the other hand,
once we cross a threshold (exceed the resilience) there may be a dramatic
and essentially irreversible shift in the fundamental processes of the
system.

Systems View Simulations of the Possible Scenarios

One aspect of the systems view that is very useful is the construction
of simulation models that will predict what will happen if the current
processes continue at the same rate. A simple simulation is the projection
of when oil or natural gas reserves will be depleted if they are consumed
at the same rate as they are now compared to if there is the same rate
of growth of the consumption. This is a very enlightening comparison that
shows that a resource that might last 200 years at the current rate of
consumption (barrels of oil per year for example) might only last 50 years
if we project that the rate of growth of consumption continues at 5% per
year.

We have seen other examples of this type of modeling when we studied
population growth models. Pure exponential growth occurs if we assume
that the growth rate remains unchanged, whereas the "logistic"
equation is on example of the pattern of growth that factors in reduced
growth rate as resources are depleted. Variations on the "logistic"
model include boom and bust cycles or irruptive growth.

Similar, but more involved, simulations can be constructed for human
population growth, energy resource depletion, pollution, and quality of
life indicators. Donella Meadows and colleagues (Meadows et al. 1992)
have created very large models that project future scenarios based on
current consumption and growth rates and slight variations in those assumptions.
They have used these to explore possible future scenarios and examine
characteristics of systems that lead to global collapse compared to the
characteristics of systems that lead to sustainable societies. Figure
2 presents a cartoon of one of their comparison.

Figure 2a. In this scenario the initial resources are lower which leads
to a moderate rise in population. As resources are depleted, industrial
output only creates a low level of pollution which is eventually reduced.
The population goes through a minor correction as expected from the
industrial transition.

Figure 2b. In this simulation, higher initial resources lead to more
rapid population growth and the level of pollution reaches as level
that is high enough to degrade natural resources, including food production.
The drop in resources and pollution lead to a major correction, i.e.
bust, in the population.

Both of these scenarios are equally probably but one is much more desirable.
The simulation shows illustrates the importance of containing a potentially
positive feedback between increased population leading to increased pollution
which destroys food production capacity and leads to an overshoot in population
and a crash. Although we may see a population crash as a "natural"
correction in human population, the causes and circumstances (environmental
degradation and starvation) would probably be considered very undesirable
future for most people.

Choosing Between Scenarios

Each scenario represents a set of initial conditions and response parameters
that are theoretically under human social control. The choice of strategy
can be portrayed as a "game against nature", where each strategy
that you choose has different outcomes depending on uncertain natural
events. Figure 3 was presented earlier in the "games view" as
a game against nature.

No tornado

Tornado comes right down your street

You - spend money to prepare for
a bad tornado

You "wasted" your money

You suffered only minor damage and lived through the
storm

You - spend the money on a new TV

You didn't waste your money and you have a cool TV
in front of your lounger

Your house is wrecked and it isn't the same watching
your TV from a folding chair

Figure 3. A simple game against nature.

In the present case study, you choices are more sophisticated strategies
for managing natural resources and reducing pollution impact, and the
natural uncertainty has to do with the global biogeochemical cycle response
to resources, pollution and human population. For the purposes of this
case study, the pollution is the general CO2 increase in the atmosphere
caused by increased energy use and poor land use management. The choices
might be represented by the game against nature shown in Figure 4.

You suffered only minor damage and lived through the
worst of global degradation

You - spend the money increasing
industrial growth

You didn't waste your money and you have a bigger
economy with more TVs to sell.

Your population crashes, your economy is wrecked,
Hollywood is underwater and there's nothing good on TV.

Figure 4. The "game against nature" modified to show how
dealing with CO2 pollution might be the best strategy. Many people would
rationally choose the strategy that results in the least bad outcome,
the "maximin" solution.